Re: [PATCH] acpi: pci_root: fix NULL pointer deref after resume from suspend

Rafael J. Wysocki
2009-09-28T20:42:26Z

On Monday 28 September 2009, Alex Chiang wrote:
> Hi Xiaotian,
>
> Thanks for the bug report.
>
> * Xiaotian Feng <dfeng@redhat.com>:
> > commit 275582 introduces acpi_get_pci_dev(), but pdev->subordinate
> > can be NULL, then a NULL was passed to pci_get_slot, this results
> > the kernel oops when resume from suspend.
> >
> > This patch resolves following kernel oops:
> > BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
> > IP: [<ffffffff812217e7>] pci_get_slot+0x4c/0x8c
> >
> > Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
> > ---
> > drivers/acpi/pci_root.c | 6 +++++-
> > 1 files changed, 5 insertions(+), 1 deletions(-)
> >
> > diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> > index 3112221..3c35144 100644
> > --- a/drivers/acpi/pci_root.c
> > +++ b/drivers/acpi/pci_root.c
> > @@ -387,7 +387,11 @@ struct pci_dev *acpi_get_pci_dev(acpi_handle handle)
> > if (!pdev || hnd == handle)
> > break;
> >
> > - pbus = pdev->subordinate;
> > + if (pdev->subordinate)
> > + pbus = pdev->subordinate;
> > + else
> > + pbus = pdev->bus;
> > +
>
> I'm a little confused by this. If we start from the PCI root
> bridge and walk back down the hierarchy, shouldn't everything
> between the root and the device be a P2P bridge?

Well, if my reading of the code is correct, there's no guarantee that
pci_get_slot() will always return either the right device or a bridge. If it
returns anything that's not a bridge or the device we're looking for, we'll hit
the NULL pointer deref.

In fact it looks like we should also clear pdev if no device was found.

Thanks,
Rafael